There have been developments of various techniques for surface treatment methods of forming a covering film on a treating portion of work such as an engine component, involving recent active developments, in particular, of discharge surface treatment methods using discharge energy (Japanese Patent Application Laying-Open Publication Nos. 8-300227 and 2005-213554).
These discharge surface treatment methods included using a compression-molded compact (a coating block) of powder of metal or the like as an electrode, generating pulsed discharges between the electrode and a treating portion of work in working oil. This involved making use of attendant discharge energy, causing molten pieces of an electrode material or reactants of the electrode material to be showered onto the treating portion of work, affording to form a covering film onto the treating portion of work.